§Parental investment is all about ensuring the infant survives. The parents need this to happen for their genetic material to be passed on. §But what if the off-spring have different needs? §What if the child’s needs mean the parents health suffers?
§Children desire greater investment than their parents have been selected to provide. §Parents try to allocate resources to their offspring in order to ensure that the maximum number of offspring survive. §However, conflict occurs when each child wants more resources than the parent is prepared to give.
Conflict before birth
§Mother needs to stay health but foetus makes huge demands on her body. §? Morning sickness is the baby stopping the mum from eating toxic food. §Pregnancy-induced diabetes might be the infant wanting more glucose. §High BP could be the infant wanting more nutrients (more blood flow).
Conflict after birth
§Weaning conflict §Change in amount of time invested by parents. §Sibling rivalry.
§The child will want to delay weaning as long as possible, often in contrast to mother’s wishes §Point of weaning coincides with time mother ready to breed again, earlier than the time infant thinks it should be!
Parental time investment
§More time invested when infants small and helpless §Limited resources directed away from older children §Conflict increases as this happens §First and last born get most attention §Support from Andrews 2000, severe suicide attempts more likely in middle children – extreme way to get parental attention
How do kids ‘fight back’?
§Trivers 1974, temper tantrums coincide with parent decreasing investment. §It’s really hard to wean a child (at any age)! §Hostile attitude to new sibling §Children ‘regress’ back to earlier behaviours to try and persuade parent they still need looking after
Competition between siblings
§According to Buss (1999) §Parents encourage their children to value their siblings more than they naturally would §Parents punish conflict between siblings and reward co-operation, against the child’s natural instincts.
Conflict at puberty
§Conflict can re-emerge when child reaches sexual maturity. §Inclusive fitness (Flinn 1989), better for mother to have another child herself than become a grandmother (50% genetic similarity vs 25%), so doesn’t want daughter to reproduce. §Flinn 1989, mother-daughter conflict higher when mother of reproductive age in Trinidad
Even later conflict!
§Parents want children to reproduce with someone who is going to maximise the fitness of their grandchildren! §They want children to engage in long-term not short-term mating. §‘Grandmother hypothesis’ – women past child rearing age invest in grandchildren so want their son/daughter-in law to mate with someone who will produce healthy offspring.
§Conflict after birth: children don’t always compete – sometimes they opt out and form alliances with non-relatives. §Parents sometimes deal with rivalry by encouraging different strengths which might also reduce future mating competition
Female infanticide (or foeticide): rare in humans usually involves killing female babies reflects low status of women in some parts of the world (e.g. China 1 child policy). Stepfathers are more likely to kill or abuse their stepchildren: as indicated by samples of children dying before the age of 15 and samples of children suffering head and other injuries (Daly and Wilson, 1994) Younger mothers are more likely to kill their infants than are older mothers, even when financial resources and marital status are held constant, (Daly and Wilson, 1988), Older mothers are less likely to abuse or harm their infants (Daly and Wilson, 1985) Animal infanticide: Seen in primates where there is lots of competition, kill the infant then the female has to mate again.
Evaluation of POC theory
§Empirical support: §Cross-cultural research suggests parental investment is lower §in families with at least 1 step-parent; §when fathers question their paternity; §when infants are ill, weak or deformed; §during periods of famine; §when families are poor or lack social support; §when mothers are very young; §when families have too many children; §when birthing space is too short (Daly and Wilson, 1984)
§Lack of evidence among human groups, lots of animal studies. §Most evidence from small samples with methodological issues.